Objectives This study aimed to establish consensus on items to be included in professional guidelines supporting clinical practitioners and community organisations to effectively implement physical activity (PA) interventions for children and young people with intellectual and developmental disabilities.

Methods A modified Delphi study was conducted in two stages. First, a roundtable discussion was held with a steering panel of 12 experts in the field to inform initial items for consideration within the Delphi survey. This was followed by a two-round survey of a wider panel of international experts to establish consensus of agreement on the items that should be included in implementation guidelines for PA interventions for this population ensuring relevance across geographical and cultural contexts.

Results 46 experts from eight countries, academics and practitioners in the field of PA took part. Consensus was reached on 73 items for inclusion in implementation guidelines. These included items related to context for the PA (eg, familiar spaces, community needs assessments and marginalised communities), activities to support implementation (PA prioritisation and facilitator training) and key outcomes to measure from individual (eg, participation in and enjoyment of PA) to systems level (eg, drop-out, reach and number of PA opportunities).

Conclusion The items identified through this study will be incorporated into professional guidelines supporting effective and sustainable implementation of PA interventions for children with intellectual and developmental disabilities. This will include using cross-sector collaboration between health, education and community services; workforce training and support; accessible infrastructure and resources; family engagement; and system-level monitoring and evaluation.